When a group of electrical workers are sent to investigate a bizarre power source coming from an abandoned Chicago building, they inadvertently come across a deserted laboratory. Inside this laboratory is what they think is a defunct nuclear power core, until it is accidentally activated, opening up a portal to a parallel universe.
Suddenly, they are trapped in a maddening mirror-world where savage, cannibalistic humans with spider appendages stalk and swarm. Here, a dwindling band of survivors fight back with primitive weapons against the growing storm of spider-people and their monstrous queen. These two groups must join forces to defeat the queen and find their way through the portal away from this terrifying and treacherous parallel universe.